Recently, with the widespread use of wireless information terminals such as cellular phones, and the development of position information acquisition technology by wireless technology and GPS (Global Positioning System), information delivery service combined with position information has been brought into operation. Users transmit position information to carriers or service providers tying up with the carriers, thereby enjoying service of delivery of information and contents in accordance with the position information. The information and contents in accordance with position information are, for example, a map, a weather forecast, and traffic information in the vicinity of a current position.
Users enjoy information delivery service by push-type and pull-type methods. With the pull-type method, the users issue an information delivery request to a service provider, which starts information delivery upon receipt of the request. On the other hand, regardless of users' requests, the service provider delivers information without permission upon some change of user status. As a push-type information delivery method, the method of delivering specific contents based on users' position information is particularly in widespread use. For example, if users subscribe to their favorite channels (weather forecast channel, local news channel, etc.), from that time onward, without waiting for position information from the users, position information is transmitted to a carrier or a contents provider tying up with the carrier, and information suitable for the user's position information is selected from among contents of the channels and delivered.
User participatory position information service is also available. According to this service, without unidirectionally receiving information delivery, users can transmit information of their own will. For example, users register messages to be transmitted in a dedicated server together with their position information, and the registered messages are transmitted to other users whose current position satisfies specific conditions.
Presently, the above-mentioned position information, together with other user attribute information (e.g., name, age, sex, etc.), is often represented by the term presence information. Presently, various services using presence information are devised, and services using presence information will come into widespread use in future. As of this point in time, the most popular service is an instant messenger. To use the instant messenger, users install dedicated software in a terminal and start the software to connect to a network. Then, since it can be determined whether a communication party connects currently to the network, if the communication party has started the same software, messages can be exchanged in real time.
Accordingly, to use the instant messenger, the users must provide their presence information indicating whether they connect to the network, and further acquire presence information of the communication party as well. Hence, the users must have an account on presence service provided by service providers. Such an account is refereed to as presentity. Also in this specification, the term presentity will be used in descriptions below. The users have a list (hereinafter referred to as a buddy list) for registering and managing presentities of communication parties, and exchange presence information with presentities included in the buddy list.
To register a presentity in the buddy list, using the identifier of presentity of a communication party (hereinafter referred to as a presentity identifier) obtained by some method, push-type notification of presence information to the presentity is filed. Hereinafter, this is referred to as subscribe. If users subscribe to the communication party, the fact is notified to the party through a presence server or directly from the users, and the party can determine whether the presence information should be released, for each of the users. Most of instant messages using presence service by using this mechanism have a function for preventing spam by shutting out messages from other than presentities registered in the buddy list.
A recent investigation has reported that the utilization rate of instant messengers as PC applications have exceeded that of Web browsers. In future, such software will come into widespread use as an application of cellular phones. With the forecast in view, standardization groups such as IETF (Internet Engineering Task Force) is studying a system for handling users' position information as part of presence information.